The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Fuel efficiency and emission control are important factors in modern vehicle design and control strategies. A number of strategies have been developed to enhance vehicle performance to improve these factors, including but not limited to hybrid energy usage, alternative engine control strategies, adjusting shift schedules, and utilizing various aftertreatment strategies. These strategies collectively strive to reduce fuel consumption and control undesirable by-products expelled from the vehicle as exhaust.
Known powertrain architectures utilizing hybrid energy sources include torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output member. One exemplary powertrain includes a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Electric machines, operative as motors or generators, generate a torque input to the transmission, independently of a torque input from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed. Strategies for balancing the different highly efficient operation under electrical power and high output operation under combustion are known, and these balancing strategies allow for flexibility through different operating conditions. Through modulation of the various components of the powertrain, the vehicle can take advantage of operating conditions especially beneficial to particular modes of operation, reclaim kinetic energy as potential energy, and store that potential energy in an energy storage device, thereby allowing storage and later low or zero emission use of energy that would normally be dissipated through vehicle braking.
Engine control strategies utilized to enhance vehicle performance take many forms. New engine mechanisms provide means to increase efficiency. For example, active fuel management including cylinder deactivation is known wherein a vehicle control system determines a required torque input from the engine, and only utilizes the proportion of cylinders in the engine necessary to efficiently deliver that torque. Another example includes enhanced engine valve operation, for instance, variable lift valves, enabling unthrottled operation controlling air intake by the opening of the valves, thereby reducing pumping losses associated with throttled operation. Also, variable valve timing in combination with variable spark timing and enabling engine control mechanisms allow manipulation of the combustion cycle to match optimal combustion for particular operating conditions. Additionally, advanced engines include a variety of control strategies, for example, taking advantage of in-cylinder pressure sensing and high speed processing to optimize and adjust combustion from cycle to cycle. Additionally, new combustion processes provide flexible combustion parameters with different optimal ranges. Combustion within conventional gasoline and diesel engines was long performed at stoichiometric and lean fuel air ratio, respectively, providing a mixture of the two chemical components (fuel and oxidizer) necessary to sustain a desired combustion reaction. Other combustion processes are known, for example, homogeneous charge compression ignition (HCCI), pre-mixed charge compression ignition (PCCI) and stratified charge spark ignition direct-injection (stratified-charge SIDI), by taking advantage of unconventional charge concentrations, charge mixtures, and ignition methods to more efficiently extract energy from the charge. Each of the above improvements to engine control strategies are highly dependent upon vehicle operating conditions, such as engine speed and engine load.
Each combustion process includes ranges and conditions necessary or favorable to efficient operation. For example, HCCI combustion requires an internal combustion engine designed to operate under an Otto cycle. The engine, equipped with direct in-cylinder fuel-injection, operates in a controlled auto-ignition mode under specific engine operating conditions to achieve improved engine fuel efficiency. A spark ignition system is employed to supplement the auto-ignition combustion process during specific operating conditions.
An HCCI engine operating in HCCI combustion mode creates a charge mixture of combusted gases, air, and fuel in a combustion chamber, and auto-ignition is initiated simultaneously from many ignition sites within the charge mixture during a compression stroke, resulting in stable power output, high thermal efficiency and low emissions. The combustion is highly diluted and uniformly distributed throughout the charge mixture, resulting in low burnt gas temperature and NOx emissions typically substantially lower than NOx emissions of either a traditional spark ignition engine, or a traditional diesel engine.
HCCI has been demonstrated in two-stroke gasoline engines using conventional compression ratios. It is believed that the high proportion of burnt gases remaining from the previous cycle, i.e., the residual content, within the two-stroke engine combustion chamber is responsible for providing the high mixture temperature necessary to promote auto-ignition in a highly diluted mixture.
In four-stroke engines with traditional valve means, the residual content is low and HCCI at part load is difficult to achieve. Known methods to induce HCCI at low and part loads include: 1) intake air heating, 2) variable compression ratio, and 3) blending gasoline with ignition promoters to create a more easily ignitable mixture than gasoline. In all the above methods, the range of engine speeds and loads in which HCCI can be achieved is relatively narrow. Extended range HCCI has been demonstrated in four-stroke gasoline engines using variable valve actuation with certain valve control strategies that effect a high proportion of residual combustion products from a previous combustion cycle necessary for HCCI in a highly diluted mixture. With such valve strategies, the range of engine speeds and loads in which HCCI can be achieved is greatly expanded using a conventional compression ratio. One such valve strategy includes trapping and recompression of exhaust gases by early closure of the exhaust valve during the exhaust stroke and low valve lift. Such valve control can be implemented using variable cam phasers and two-step lift cams.
PCCI is an engine operating mode well known in the art and is a similar engine operating mode to the aforementioned HCCI mode. One having ordinary skill in the art will appreciate that PCCI is essentially a diesel equivalent to HCCI operated in gasoline engines. Diesel engines operating in particular speed and load ranges and running in a PCCI mode can realize advantageous engine emissions result in comparison to diesel engines operating under conventional lean operation.
Stratified charge SIDI (stratified-charge SIDI) is also an engine combustion mode well known in the art and is a means to improve engine performance under particular operating conditions. One having ordinary skill in the art will appreciate that stratified-charge SIDI includes, within a particular operating range, managing the concentration and pattern of fuel-air mixture around the spark plug at the spark time using direct in-cylinder gasoline injection and intentionally creating an efficient combustion event acting upon the piston, thereby increasing the engine efficiency.
The above described engine combustion processes to enhance vehicle performance are highly dependent upon engine design and vehicle operating conditions, in particular, the engine speeds and engine loads demanded of the engine. A number of methods are contemplated to process information available from vehicle sensors, such as vehicle speed, engine speed, output torque, etc., in order to predictively estimate vehicle operating conditions to facilitate efficient and low emission vehicle operation. Such methods can estimate changing conditions and their effects upon the vehicle in the short term based upon changes and the rates of change of readings from the vehicle sensors. While these short term predictions of vehicle operating conditions are useful to modulating immediate combustion modes and reactions, they are still essentially reactionary.
Various electronic means of tracking vehicle position and coordinating vehicle position with geographic, road, traffic, or other information are known. Monitoring such data is commonly known as utilizing map preview information. Preferred and accessible electronic means to accomplish such data acquisition includes global position systems (GPS) in coordination with electronic maps, digital map software using means to track the movement of the vehicle, internet-based wireless-accessible data processing, vehicle to vehicle communications, and vehicle to infrastructure communications and other remote computing resources. These electronic means provide a wide variety of information which can be used to adjust vehicle and engine operations based upon the particulars of the environment in which the vehicle is operating or likely to soon operate. Information from such systems include: road classification, such as highway, local road, parking lot, gravel road, etc.; speed limits for various stretches of road; traffic conditions for various stretches of road, including real-time evaluations of congestion, signals sent from cooperating vehicles experiencing traffic, analysis of cellular phone patterns in other cars, predictions based upon likely rush hour traffic or special event (e.g. sporting event) traffic; road slopes; road curvature; location and status of traffic lights, signals, construction zone markers, speed bumps, or other traffic direction indicators impacting vehicular travel; existence or lack of features likely to impact travel along a certain stretch of road, such as exit ramps or truck weigh stations; and analysis of vehicle or specific operator driving patterns, habits, registered schedules, electronic planner calendars, or other predictive measures. Additionally, likely routes of travel can be estimated based upon operator entered destinations, computerized analysis of driver habits and patterns, or other means.